Deuterium Substituted Fumarate Derivatives

ABSTRACT

Provided is a compound of formula (I): 
     
       
         
         
             
             
         
       
     
     or a pharmaceutically acceptable salt thereof. Also provided is a method of activating the Nrf2 pathway, comprising contacting cells with a sufficient amount of a compound of formula (I) described herein. Also provided is a method of treating a neurodegenerative disease, comprising administering to a subject in need of treatment for the neurodegenerative disease an effective amount of a compound of formula (I) described herein.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY VIA EFS-WEB

The content of the electronically submitted sequence listing (Name: 2159_(—)4340001_SequenceListing_ascii.txt; Size: 493 bytes; Date of Creation: Dec. 18, 2013) filed with the application is incorporated herein by reference in its entirety.

BACKGROUND

BG-12 (dimethyl fumarate) is currently undergoing regulatory review as a potential oral treatment for multiple sclerosis (MS), following the completion of two large Phase 3 studies in patients with relapsing-remitting MS (RRMS). The first Phase 3 study, DEFINE (ClinicalTrials.gov identifier NCT00420212), demonstrated that BG-12 significantly reduced clinical relapses, accumulation of disability progression, and lesion number and volume compared with placebo after two years of treatment. See, e.g., Gold R, et al. N Engl J Med 2012; 367: 1098-107. These findings were supported by the results of the second phase 3 study, CONFIRM, which additionally evaluated subcutaneous glatiramer acetate as an active reference treatment (rater-blind). See, e.g., Fox R J, et al. N Engl J Med 2012; 367: 1087-97.

Preclinical and clinical data suggest dimethyl fumarate (DMF) has beneficial effects on neuroinflammation, neurodegeneration, and toxic-oxidative stress. See, e.g., Linker R. A., et al., Brain 2011; 134:678-92 and Scannevin R. H., et al., J Pharmacol Exp Ther 2012, 341:274-284. The beneficial effects of DMF and its primary metabolite, monomethyl fumarate (MMF), appear to be mediated, at least in part, through activation of the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) antioxidant response pathway, an important cellular defense. Nrf2 is expressed ubiquitously in a range of tissues and, under normal basal conditions, is sequestered in the cytoplasm in a complex with Keap1 protein. However, when cells are under oxidative stress and overloaded with reactive oxygen or nitrogen species (ROS or RNS), or electrophilic entities, Nrf2 rapidly translocates to the nucleus, forms heterodimer with small protein Maf, then binds to the antioxidant response element, resulting in increased transcription of several antioxidant and detoxifying genes including NQO-1, HO-1, and SRXN1. See, e.g., Nguyen et al., Annu Rev Pharmacol Toxicol 2003; 43:233-260; McMahon et al., Cancer Res 2001; 61:3299-3307. Sustained oxidative stress has been implicated in the pathogenesis of a variety of neurodegenerative diseases such as MS, amyotrophic lateral sclerosis (ALS), Alzheimer's disease, and Parkinson's disease. For reviews, see, e.g., van Muiswinkel et al., Curr. Drug Targets CNS—Neurol. Disord, 2005; 4:267-281; Burton N. C. et al., Comprehensive Toxicology, 2010, 59-69.

DMF quickly gets absorbed in vivo and converted to MMF. The half-life of MMF was shown to be approximately 1 hour (0.9 h in rat at 100 mg/Kg oral dose). Both DMF and MMF are metabolized by esterases which are ubiquitous in the GI tract, blood and tissues.

BG-12 has demonstrated an acceptable safety profile in the DEFINE and CONFIRM studies. However, tolerability issues such as flushing and gastrointestinal events were observed. While these events are generally mild to moderate in severity, there remains a desire to reduce such events to further increase patient compliance and improve patient's quality of life. These mild adverse events could be the result of off-target events induced either by DMF or MMF and or the metabolites derived from them. For example, recent reports (Hanson et al., J. Clin. Invest. 2010, 120, 2910-2919; Hanson et al., Pharmacol. Ther. 2012, 136, 1-7.) indicate that MMF induced flushing is due to the activation of the G-protein-coupled receptor HCA2 (Hydroxy-carboxylic acid receptor 2, GPR109A).

There is a need for BG-12 analogs having an improved pharmacokinetic profile.

SUMMARY

Provided is a compound of formula (I):

or a pharmaceutically acceptable salt thereof, wherein

each of R¹ and R², independently, is hydrogen, deuterium, deuterated methyl, deuterated ethyl, C₁₋₆ aliphatic, phenyl, 3-7 membered saturated or partially unsaturated monocyclic carbocyclic ring, 3-7 membered saturated or partially unsaturated monocyclic heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, or a 5-6 membered heteroaryl ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, and

each of R³ and R⁴, independently, is hydrogen or deuterium, provided that the compound of formula (I) contains at least one deuterium atom and that R¹ and R² are not hydrogen at the same time.

Also provided is a method of activating the Nrf2 pathway, comprising contacting cells with a sufficient amount of a compound of formula (I) described herein.

Also provided is a method of treating a neurodegenerative disease, comprising administering to a subject in need of treatment for the neurodegenerative disease an effective amount of a compound of formula (I) described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a)-(c) describe the PD response of DMF and compounds of Examples 1 and 2.

DETAILED DESCRIPTION Definitions

Certain terms are defined in this section; additional definitions are provided throughout the description.

The term “aliphatic” or “aliphatic group”, as used herein, means a straight-chain (i.e., unbranched) or branched, substituted or unsubstituted hydrocarbon chain that is completely saturated or that contains one or more units of unsaturation. Unless otherwise specified, aliphatic groups are optionally substituted and contain 1-6 aliphatic carbon atoms. In some embodiments, aliphatic groups contain 1-5 aliphatic carbon atoms. In some embodiments, aliphatic groups contain 1-4 aliphatic carbon atoms. In some embodiments, aliphatic groups contain 1-3 aliphatic carbon atoms, and in yet other embodiments, aliphatic groups contain 1-2 aliphatic carbon atoms. Suitable aliphatic groups include, but are not limited to, linear or branched, substituted or unsubstituted alkyl, alkenyl, alkynyl groups and hybrids thereof.

The term “carbocycle,” “carbocyclic,” or “cycloaliphatic,” as used herein, means a monocyclic hydrocarbon that is completely saturated or that contains one or more units of unsaturation, but which is not aromatic (also referred to herein as “ ”), that has a single point of attachment to the rest of the molecule. Unless otherwise specified, carbocyclic groups are optionally substituted. Examples include cycloalkyl and cycloalkenyl. In some embodiments, aliphatic groups contain 3-7 aliphatic carbon atoms. In some embodiments, aliphatic groups contain 4-6 aliphatic carbon atoms. In some embodiments, aliphatic groups contain 5-6 aliphatic carbon atoms, and in yet other embodiments, aliphatic groups contain 6 aliphatic carbon atoms.

The term “heteroaryl,” as used herein, refers to groups having 5 to 6 ring atoms, sharing π electrons in a cyclic array; and having, in addition to carbon atoms, from 1-3 heteroatoms. The term “heteroatom” refers to nitrogen, oxygen, or sulfur, and includes any oxidized form of nitrogen or sulfur, and any quaternized form of a basic nitrogen. Heteroaryl groups include, without limitation, thienyl, furanyl, pyrrolyl, imidazolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, isothiazolyl, thiadiazolyl, pyridyl, pyridazinyl, pyrimidinyl, and pyrazinyl. Unless otherwise specified, heteroaryl groups are optionally substituted.

As used herein, the terms “heterocycle,” “heterocyclyl,” “heterocyclic radical,” and “heterocyclic ring” are used interchangeably and refer to a stable 5- to 7-membered monocyclic moiety that is either saturated or partially unsaturated, and having, in addition to carbon atoms, 1-3 heteroatoms, as defined above. When used in reference to a ring atom of a heterocycle, the term “nitrogen” includes a substituted nitrogen. As an example, the nitrogen may be N (as in 3,4-dihydro-2H-pyrrolyl), NH (as in pyrrolidinyl), or ⁺NR (as in N-substituted pyrrolidinyl).

A heterocyclic ring can be attached to its pendant group at any heteroatom or carbon atom that results in a stable structure and any of the ring atoms can be optionally substituted. Examples of such saturated or partially unsaturated heterocyclic radicals include, without limitation, tetrahydrofuranyl, tetrahydrothiophenyl pyrrolidinyl, piperidinyl, pyrrolinyl, oxazolidinyl, piperazinyl, dioxanyl, dioxolanyl, diazepinyl, oxazepinyl, thiazepinyl, and morpholinyl.

As described herein, compounds of the invention may, when specified, contain “optionally substituted” moieties. In general, the term “substituted,” whether preceded by the term “optionally” or not, means that one or more hydrogens of the designated moiety are replaced with a suitable substituent. Unless otherwise indicated, an “optionally substituted” group may have a suitable substituent at each substitutable position of the group, and when more than one position in any given structure may be substituted with more than one substituent selected from a specified group, the substituent may be either the same or different at every position. Combinations of substituents envisioned by this invention are preferably those that result in the formation of stable or chemically feasible compounds. The term “stable,” as used herein, refers to compounds that are not substantially altered when subjected to conditions to allow for their production, detection, and, in certain embodiments, their recovery, purification, and use for one or more of the purposes disclosed herein.

Examples of optionally substituted groups include halogen, —NO₂, —CN, —OR, —SR, —N(R)₂, —C(O)R, —CO₂R, —N(R)C(O)OR, —C(O)N(R)₂, —OC(O)R, —N(R)C(O)R, —S(O)R, —S(O)₂R, or —S(O)₂N(R)₂. Each R is independently hydrogen or C₁₋₆ aliphatic; or two R groups attached to the same nitrogen are taken together with their intervening atoms to form an optionally substituted 3-7 membered saturated or partially unsaturated monocyclic heterocyclic ring having 1-2 heteroatoms, independently selected from nitrogen, oxygen, or sulfur. Optionally substituted groups of aliphatic can further include phenyl, 3-7 membered saturated or partially unsaturated monocyclic carbocyclic ring, 3-7 membered saturated or partially unsaturated monocyclic heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or a 5-6 membered heteroaryl ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, or sulfur. For example, cycloalkyl)alkyl, (cycloalkenyl)alkyl or (cycloalkyl)alkenyl, heterocyclylalkyl. Optionally substituted groups of phenyl, heterocycle, carbocycle, and heteroaryl can further include optionally substituted aliphatic groups.

The term “deuterium enrichment factor”, as used herein, means the ratio between the isotopic abundance and the natural abundance of deuterium.

In a compound of this invention, when a particular position is designated as having deuterium, it is understood that the abundance of deuterium at that position is substantially greater than the natural abundance of deuterium, which is 0.015%. A position designated as having deuterium typically has a minimum isotopic enrichment factor of at least 3340 (50.1% deuterium incorporation) at each atom designated as deuterium in said compound.

In other embodiments, a compound of this invention has an isotopic enrichment factor for each designated deuterium atom of at least 3500 (52.5% deuterium incorporation at each designated deuterium atom), at least 4000 (60% deuterium incorporation), at least 4500 (67.5% deuterium incorporation), at least 5000 (75% deuterium), at least 5500 (82.5% deuterium incorporation), at least 6000 (90% deuterium incorporation), at least 6333.3 (95% deuterium incorporation), at least 6466.7 (97% deuterium incorporation), at least 6600 (99% deuterium incorporation), or at least 6633.3 (99.5% deuterium incorporation).

The terms “deuterated methyl” and “deuterated ethyl,” as used herein, means that the methyl group and the ethyl group contain at least one deuterium atom. Examples of deuterated methyl include —CDH₂, —CD₂H, and —CD₃. Examples of deuterated ethyl include —CHDCH₃, —CD₂CH₃, —CHDCDH₂,

—CH₂CD₃.

As used herein, the term “pharmaceutically acceptable salt” refers to those salts which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio. Pharmaceutically acceptable salts are well known in the art. For example, S. M. Berge et al., describe pharmaceutically acceptable salts in detail in J. Pharmaceutical Sciences, 1977, 66, 1-19, incorporated herein by reference.

In certain embodiments, the neutral forms of the compounds are regenerated by contacting the salt with a base or acid and isolating the parent compound in the conventional manner. In some embodiments, the parent form of the compound differs from the various salt forms in certain physical properties, such as solubility in polar solvents.

A “pharmaceutically acceptable carrier,” as used herein refers to pharmaceutical excipients, for example, pharmaceutically, physiologically, acceptable organic or inorganic carrier substances suitable for enteral or parenteral application that do not deleteriously react with the active agent. Suitable pharmaceutically acceptable carriers include water, salt solutions (such as Ringer's solution), alcohols, oils, gelatins, and carbohydrates such as lactose, amylose or starch, fatty acid esters, hydroxymethycellulose, and polyvinyl pyrrolidine. Such preparations can be sterilized and, if desired, mixed with auxiliary agents such as lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure, buffers, coloring, and/or aromatic substances and the like that do not deleteriously react with the compounds of the invention.

The terms “activation” and “upregulation,” when used in reference to the Nrf2 pathway, are used interchangeably herein.

The term “a drug for treating a neurological disease” refers to a compound that has a therapeutic benefit in a specified neurological disease as shown in at least one animal model of a neurological disease or in human clinical trials for the treatment of a neurological disease.

The terms “treatment,” “therapeutic method,” “therapeutic benefits,” and the like refer to therapeutic as well as prophylactic/preventative measures. Thus, those in need of treatment may include individuals already having a specified disease and those who are at risk for acquiring that disease.

The terms “therapeutically effective dose” and “therapeutically effective amount” refer to that amount of a compound which results in prevention or delay of onset or amelioration of symptoms of a neurological disorder in a subject or an attainment of a desired biological outcome, such as reduced neurodegeneration (e.g., demyelination, axonal loss, and neuronal death), reduced inflammation of the cells of the CNS, or reduced tissue injury caused by oxidative stress and/or inflammation in a variety of cells.

Compounds

Provided is a compound of formula (I)

or a pharmaceutically acceptable salt thereof, wherein

each of R¹ and R², independently, is hydrogen, deuterium, deuterated methyl, deuterated ethyl, C₁₋₆ aliphatic, phenyl, 3-7 membered saturated or partially unsaturated monocyclic carbocyclic ring, 3-7 membered saturated or partially unsaturated monocyclic heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, or a 5-6 membered heteroaryl ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, and

each of R³ and R⁴, independently, is hydrogen or deuterium, provided that the compound of formula (I) contains at least one deuterium atom and that R¹ and R² are not hydrogen at the same time.

Also provided is a compound of formula (I)

or a pharmaceutically acceptable salt thereof. wherein

each of R¹ and R², independently, is hydrogen, deuterium, deuterated methyl, deuterated ethyl, or C₁₋₆ aliphatic, and

each of R³ and R⁴, independently, is hydrogen or deuterium, provided that the compound of formula (I) contains at least one deuterium atom and that R¹ and R² are not hydrogen at the same time.

In some embodiments, R¹ is hydrogen or —CH₃. In some embodiments, R¹ is —CD₃. In some embodiments, R¹ is —CD₂CD₃.

In some embodiments, R² is —CH₂D, —CHD₂, or —CD₃. In some embodiments, R² is H, —CH₃, —CH₂D, —CHD₂, or —CD₃.

In some embodiments, R¹ is hydrogen or —CH₃ and R² is —CH₂D,

—CHD₂, or —CD₃.

In some embodiments, R¹ is —CD₃ and R² is —CH₂D, —CHD₂, or —CD₃.

In some embodiments, at least one of R³ and R⁴ is deuterium. In some embodiments, both of R³ and R⁴ are deuterium.

In some embodiments, at least one of R³ and R⁴ is deuterium and R² is hydrogen, —CH₃, —CH₂D, —CHD₂, or —CD₃. In some embodiments, both of R³ and R⁴ are deuterium and R² is hydrogen, —CH₃, —CH₂D, —CHD₂, or —CD₃.

In some embodiments, R¹ is —CD₂CD₃ and R² is H, —CH₃, —CH₂D,

—CHD₂, or —CD₃

In some embodiments, the compound of formula (I) is (²H₆)dimethyl fumaric acid ester, (²H₃)methyl fumaric acid ester, (²H₃)dimethyl fumaric acid ester, or dimethyl fumaric(2,3-²H₂) acid ester.

In some embodiments, the compound of formula (I) is more resistant to CYP450 enzymes as compared with compounds of similar structure but lacking deuterium substitution.

In some embodiments, the compound of formula (I) will have slightly altered and slower metabolism as compared with compounds of similar structure but lacking deuterium substitution.

In some embodiments, the compound of formula (I) will have longer duration of action and/or improved side effect profile as compared with compounds of similar structure but lacking deuterium substitution.

(²H₆)Dimethyl fumaric acid ester (Example 1) and (²H₃)methylfumaric acid ester (Example 2) have demonstrated longer half-life of 3 to 3.2 hours, respectively, compared to DMF and MMF in rat, when given an oral dose of 100 mg/kg.

Methods of Making

Compounds of formula (I) can be synthesized, for example, using the following schemes.

As depicted in Scheme A above, fumaric acid 1 can be converted to the monohydrogen (²H₃)methyl fumaric acid ester 2 by reacting with deuterated methanol under the catalytic condition of p-toluenesulfonic acid at room temperature. At, for example, elevated temperature and similarly catalyzed by, e.g., p-toluenesulfonic acid, ester 2 can react with a variety of alcohols R¹OH (e.g., CH₃OH, CH₂DOH, CHD₂OH, CD₃OH, CD₃CH₂OH, or other deuterated alcohols) to provide deuterated fumaric acid esters of Formula Ia. Alternatively, treatment of compound 2 under coupling conditions, such as hydroxybenzotriazole (HOBT), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI), and diisopropylethylamine (DIPEA) with alcohol R¹OH will afford acid esters of Formula Ia.

Compounds of formula (I) can contain deuterium connecting to one or both carbons of the double bond. See Scheme B below.

Starting with deuterated fumaric acid 3 (wherein A can be D or H; when A is D, the compound is available from Sigma-Aldrich (CAS#24461-32-3) and when A is H, the compound can be prepared according to Tetrahedron Lett. 1988, 29(36), 4577, compounds of Formula 1b can be prepared in two steps by first reacting with CD₃OD at room temperature under, e.g., the catalytic condition of p-toluene sulfonic acid followed by subsequent esterification with alcohol R¹OH (e.g., CH₃OH, CH₂DOH, CHD₂OH, CD₃OH, CD₃CH₂OH, or other deuterated alcohols) using either Method A or B. Compounds of Formula Ic can be prepared by reacting 3 with a variety of alcohol R¹OH under catalytic acid condition at ambient temperature. Treatment of compounds of Formula Ic under the conditions of HOBT, EDCI, and DiPEA will generate diester compounds of Formula Id.

Pharmaceutical Compositions

The present invention provides pharmaceutical compositions comprising a compound of formula (I) or a compound of formula (I) in combination with a pharmaceutically acceptable excipient (e.g., carrier).

Compounds of formula (I) can be administered by any method that permits the delivery of the compound to a subject in need thereof. For instance, compounds of formula (I) can be administered by orally, intranasally, transdermally, subcutaneously, intradermally, vaginally, intraaurally, intraocularly, intramuscularly, buccally, rectally, transmucosally, or via inhalation, or intravenous administration. For oral administration, compounds of formula (I) can be administered via pills, tablets, microtablets, pellets, micropellets, capsules (e.g., containing microtablets), suppositories, liquid formulations for oral administration, and in the form of dietary supplements. Oral formulations (e.g., tablets and microtablets) can be enteric coated. In some embodiments, the mean diameter of a microtablet is about 1-5 mm, e.g., about 1-3 mm or about 2 mm.

The compositions can include well-known pharmaceutically acceptable excipients, e.g., if the composition is an aqueous solution containing the active agent, it can be an isotonic saline, 5% glucose, or others. Solubilizing agents such as cyclodextrins, or other solubilizing agents well known to those familiar with the art, can be utilized as pharmaceutical excipients for delivery of the therapeutic compound. See, e.g., U.S. Pat. Nos. 6,509,376 and 6,436,992 for some formulations containing DMF and/or MMF.

Pharmaceutically acceptable carriers can be either solid or liquid. Solid form preparations include powders, tablets, pills, capsules, cachets, suppositories, and dispersible granules. A solid carrier can be one or more substance that may also act as diluents, flavoring agents, binders, preservatives, tablet disintegrating agents, or an encapsulating material.

Carriers or excipients generally serve as fillers, disintegrants, lubricants, and glidants. Examples of suitable carriers include magnesium carbonate, magnesium stearate, croscarmellose sodium, microcrystalline cellulose, talc, silica, sugar, lactose, pectin, dextrin, starch, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose, a low melting wax, cocoa butter, and the like.

Some compounds may have limited solubility in water and therefore may require a surfactant or other appropriate co-solvent in the composition. Such co-solvents include: Polysorbate 20, 60, and 80; Pluronic F-68, F-84, and P-103; cyclodextrin; and polyoxyl 35 castor oil. Such co-solvents can be employed at a level between about 0.01% and about 2% by weight.

Viscosity greater than that of simple aqueous solutions may be desirable to decrease variability in dispensing the formulations, to decrease physical separation of components of a suspension or emulsion of formulation, and/or otherwise to improve the formulation. Such viscosity building agents include, for example, polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, hydroxy propyl methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxy propyl cellulose, chondroitin sulfate and salts thereof, hyaluronic acid and salts thereof, and combinations of the foregoing. Such agents can be employed at a level between about 0.01% and about 2% by weight.

Compounds of formula (I) can be administered in the form of a sustained or controlled release pharmaceutical formulation. Such formulation can be prepared by various technologies by a skilled person in the art. For example, the formulation can contain the therapeutic compound, a rate-controlling polymer (i.e., a material controlling the rate at which the therapeutic compound is released from the dosage form) and optionally other excipients. Some examples of rate-controlling polymers are hydroxy alkyl cellulose, hydroxypropyl alkyl cellulose (e.g., hydroxypropyl methyl cellulose, hydroxypropyl ethyl cellulose, hydroxypropyl isopropyl cellulose, hydroxypropyl butyl cellulose and hydroxypropyl hexyl cellulose), poly(ethylene)oxide, alkyl cellulose (e.g., ethyl cellulose and methyl cellulose), carboxymethyl cellulose, hydrophilic cellulose derivatives, and polyethylene glycol, and compositions as described in WO 2006/037342, WO 2007/042034, WO 2007/042035, WO 2007/006308, WO 2007/006307, and WO 2006/050730.

Nrf2 Pathway and Methods of Evaluating Nrf2 Activators

Nrf2 (Nuclear Factor-Erythroid 2-related factor 2; for sequence of the Nrf2, see Accession No. AAB32188) is the transcription factor that, upon activation by oxidative stress, forms heterodimer with small protein Maf, binds to the antioxidant response element (ARE), and activates transcription of Nrf2-regulated genes. The Nrf2/ARE pathway, a major determinant of phase II gene induction, has been well characterized for its role in hepatic detoxification and chemoprevention through the activation of phase II gene expression. ARE-regulated genes may also contribute to the maintenance of redox homeostasis by serving as endogenous anti-oxidant systems. At present, the list of Nrf2-regulated genes contains over 200 genes encoding proteins and enzymes involved in detoxification and antioxidant response (Kwak et al., J. Biol. Chem., 2003, 278:8135) such as, e.g., glutathione peroxidase, glutathione-S-transferases (GSTs), NAD(P)H:quinone oxidoreductases, now commonly known as nicotinamide quinone oxidoreductase 1 (NQO1; EC 1.6.99.2; also known as DT diaphorase and menadione reductase), NQO2, g-glutamylcysteine synthase (g-GCS), glucuronosyltransferase, ferritin, and heme oxygenase-1 (HO-1), as well as any one of the enzymes proteins listed in Table 1 in Chen & Kunsch, Curr. Pharm. Designs, 2004, 10:879-891; Lee et al., J. Biol. Chem., 2003, 278(14):12029-38, and Kwak, supra.

Accordingly, in some embodiments, the Nrf2-regulated gene which is used to assess the activation of the Nrf2 pathway is a phase II detoxification enzyme, an anti-oxidant enzyme, an enzyme of the NADPH generating system, and/or Nrf2 itself. Examples of the phase II detoxification enzymes include NQO1, NQO2, GST-Ya, GST-pi, GST-theta 2, GST-mu (1,2,3), microsomal GST 3, catalytic y-GCS, regulatory-GCS, microsomal epoxide hydrolase, UDP-glucuronosyltransferase, transaldolase, transketolase, and drug-metabolizing enzyme. Examples of the anti-oxidant enzymes include HO-1, ferritin (L), glutathione reductase, glutathione peroxidase, metallothionein I, thioredoxin, thioredoxin reductase, peroxiredoxin MSP23, Cu/Zn superoxide dismutase, and catalase. Examples of the enzymes of the NADPH generating system include malic enzyme, UDP-glucose dehydrogenase, malate oxidoreductase, and glucose-6-phosphate dehydrogenase.

Under basal conditions, Nrf2 is sequestered in the cytoplasm to the actin-bound Kelch-like ECH-associated protein 1 (Keap1; Accession No. NP_(—)987096 for human Keap1), a Cullin3 ubiquitin ligase adaptor protein. More specifically, the N-terminal domain of Nrf2, known as Neh2 domain, is thought to interact with the C-terminal Kelch-like domain of Keap1. In response to xenobiotics or oxidative stress, Nrf2 is released from the Keap1/Nrf2 complex, thereby promoting nuclear translocation of Nrf2 and concomitant activation of ARE-mediated gene transcription. Keap1 function, in turn, requires association with Cullin3, a scaffold protein that positions Keap1 and its substrate in proximity to the E3 ligase Rbx1, allowing the substrate (Nrf2) to be polyubiquitinated and thus targeted for degradation. The exact mechanism of how the Keap1/Nrf2 complex senses oxidative stress remains poorly understood. Human Keap1 contains 25 cysteine residues that were hypothesized to function as sensors of oxidative stress; 9 of the cysteines are thought to be highly reactive (Dinkova-Kostova et al., PNAS, 2005, 102(12):4584-9). It was theorized but is not relied on for the purposes of this invention that alkylation of the Keap1 cysteines leads to a conformational change, resulting in the liberation of Nrf2 from Nrf2/Keap1/Cullin3 complexes, followed by nuclear translocation of the liberated Nrf2.

As mentioned above, pre-clinical studies have also shown that DMF is neuroprotective in animal models of neuroinflammation and neurodegeneration and that it defends against oxidative stress-induced injury. In addition to Linker R. A. et al. and Scannevin R. H. et al., supra, see also Ellrichmann C, et al. PLoS One 2011; 6:e16172. The neuroprotective effects of compounds of formula (I) can be evaluated in similar studies.

For example, the neuroprotective effects of compounds of formula (I) can be investigated in the malonate striatal lesion model of excitotoxicity. Malonate is a succinate dehydrogenase inhibitor, which is a mitochondrial enzyme that plays a central role in neuronal energy metabolism. Injection of malonate into the striatal region of the brain produces a lesion that is excitotoxic in character, as it can be blocked by systemic administration of N-methyl-D-aspartate (NMDA) receptor antagonists and has little inflammatory involvement. Intrastriatal malonate injection has been used as a model for acute neurodegeneration, and the potential therapeutic effects of test compounds of formula (I) can be explored in this setting. See, e.g., Scannevin R. H. et al., poster P02.121, 64^(th) Annual Meeting of the American Academy of Neurology, Apr. 21-28, 2012, New Orleans, La., USA. The mouse cuprizone/rapamycin model of demyelination and neurodegeneration is another study that can be used to evaluate the neuroprotective effects of compounds of formula (I). Specifically, cuprizone is a neurotoxicant that when administered chronically to mice results in demyelination in the central nervous system, and has been used as a model to investigate modulation of remyelination. Administering rapamycin in addition to cuprizone results in more robust and consistent demyelination, presumably due to the anti-proliferative effect of stimulating the mammalian target of rapamycin (mTOR) receptor and pathway. The cuprizone plus rapamycin injury paradigm models prevalent pathologies (e.g., axonal transection, formation of ovoids and neuronal degeneration) associated with the human disease, and observation using this model provides unique insights into the mechanism of action of test compounds.

Diseases and Animal Models

ROS/RNS are most damaging in the brain and neuronal tissue, where they attack post-mitotic (i.e., non-dividing) cells such as glial cells and neurons, which are particularly sensitive to free radicals, leading to neuronal damage. Oxidative stress has been implicated in the pathogenesis of a variety of neurodegenerative diseases, including MS, ALS, Alzheimer's disease, Huntington disease, and Parkinson's disease. For review, see, e.g., van Muiswinkel et al., Curr. Drug Targets CNS—Neurol. Disord., 2005, 4:267-281. An anti-oxidative enzyme under control of Nrf2, NQO1 (NAD(P)H dehydrogenase, quinone 1), was reported to be substantially upregulated in the brain tissues of AD and PD subjects (Muiswinkel et al., Neurobiol. Aging, 2004, 25:1253). Similarly, increased expression of NQO1 was reported in the ALS subjects' spinal cord (Muiswinkel et al., Curr. Drug Targets—CNS. Neurol. Disord., 2005, 4:267-281) and in active and chronic lesions in the brains of patients suffering from MS (van Horssen et al., Free Radical Biol. & Med., 2006, 41:311-311). These observations indicate that the Nr12 pathway may be activated in neurodegenerative and neuroinflammatory diseases as an endogenous protective mechanism.

In one aspect, the invention provides methods of treating, slowing, or preventing a neurological disease by treating (e.g., orally administering to) a subject in need thereof one or more compounds of formula (I). Examples of such neurological diseases include MS, ALS, Alzheimer's disease, Parkinson's disease and Huntington's disease. The subject is mammalian, and can be a rodent or another laboratory animal, e.g., a non-human primate. In preferred embodiments, the subject is human.

Other examples of neurodegenerative diseases include acute haemorrhagic leucoencephalomyelitis, Hurst's disease, acute disseminated encephalomyelitis, optic neuritis, spinal cord lesions, acute necrotizing myelitis, transverse myelitis, chronic progressive myelopathy, progressive multifocal leukoencephalopathy (PML), radiation myelopathy, HTLV-1 associated myelopathy, monophasic isolated demyelination, central pontine myelinolysis, and leucodystrophy (e.g., adrenoleucodystrophy, metachromatic leucodystrophy, Krabbe's disease, Canavan's disease, Alexander's disease, Pelizaeus-Merbacher disease, vanishing white matter disease, oculodentodigital syndrome), chronic inflammatory demyelinating polyneuritis (CIDP), and acute inflammatory demyelinating polyneuropathy (AIDP). Additional examples of diseases suitable for the methods of the invention include acute Guillain-Barre syndrome (GBS), or polyneuritis), myasthenia gravis (MG), Eaton Lambert Syndrome (ELS), and encephalomyelitis. These disorders may be co-presented with, and possibly aggravated by diabetes, e.g., insulin-dependent diabetes mellitus (IDDM; type I diabetes), or other diseases.

Other diseases for which compounds of formula (I) may be therapeutically effective include inflammatory bowel disease, Crohn's disease, lupus, asthma, and other inflammatory diseases.

Activation of the Nrf2 pathway has demonstrated protective benefits in several neurodegenerative disease models. See, e.g., Calkins M J et al., Toxicoi Sci 2010; 115:557-568.

For MS, compounds of formula (I) can be assayed in well-known MS animal model, such as Experimental Autoimmune Encephalomyelitis (EAE) (Tuohy et al., J. Immunol., 1988, 141:1126-1130, Sobel et al. J. Immunol., 1984, 132:2393-2401, and Traugott, Cell Immunol., 1989 119:114-129). Chronic relapsing EAE provides a well established experimental model for testing agents that would be useful for the treatment of MS. The mouse EAE is an induced autoimmune demyelinating disease with many similarities to human MS in its clinical manifestations. Other animal models that can be used include Thieler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, murine hepatitis virus (MHV), Semliki Forest Virus, and Sindbis virus as described in, e.g., Ercoli et al., J. immunol., 2006, 175:3293-3298.

ALS is a progressive neurodegenerative disease characterized by loss of both upper and lower motor neurons leading to body and facial muscle weakness. Life expectancy is approximately 3 years post diagnosis. The unmet need is extremely high as Rilutek (riluzole) is the only approved disease modifier and offers only a modest benefit (extends survival by about 3 months). A commonly used animal model is the mouse model with ALS-linked SOD1 G93A mutation. It has been shown recently that activation of the Nrf2 pathway via genetic overexpression or pharmacological induction conferred benefit in an hSOD1 G93A animal model. See Vargas M. R., et al., J. Neurosci., 2008, 28(50):1357-13581.

Alzheimer's disease (AD) is the most common form of dementia. It is characterized by the development of extracellular amyloid-beta (Ab) plaques and intracellular neurofibrillary tangles (NFT), accompanied by decreased synaptic density, which eventually leads to widespread neurodegeneration, loss of synapses and failure of neurotransmitter pathways, particularly those of the basal forebrain cholinergic system. AD patients display prominent cognitive deficits such as memory loss, executive dysfunctioning, and behavior and psychological symptoms associated with dementia including paranoid and elusional behavior, hallucinations, anxieties and phobias. AD animal models commonly used include spontaneous models in various species, including senescence-accelerated mice, chemical and lesion-induced rodent models, and genetically modified models developed in Drosophila melanogaster, Caenorhabditis elegans, Danio rerio and rodents. For review, see, e.g., Van Dam et al., Br. J. Pharmacol. 2011, 164(4):1285-1300 and Götz et al., Nat. Rev. Neurosci. 2008, 9:532-544.

Parkinson's disease is characterized by the loss of ˜50-70% of the dopaminergic neurons in the substantia nigra pars compacta (SNc), a profound loss of dopamine (DA) in the striatum, and the presence of intracytoplasmic inclusions called Lewy bodies (LB), which are composed mainly of α-synuclein and ubiquitin. Although mutations in the α-synuclein gene have thus far been associated only with rare familial cases of PD, α-synuclein is found in all LBs. The main features of PD are tremor, rigidity, bradykinesia, and postural instability; however, these motor manifestations can be accompanied bynonmotor symptoms such as olfactory deficits, sleep impairments, and neuropsychiatric disorders. PD animal models can typically be divided into toxin-based (those produced by 6-hydroxydopamine (6-OHDA), 1-methyl-1,2,3,6-tetrahydropiridine (MPTP) rotenone, and paraquat) or genetic models such as those utilizing the in vivo expression of PD-related mutations (e.g., those related to alpha-synuclein, PINK1, Parkin and LRRK2). For review, see, e.g., Blesa et al., J. Biomed. Biotech. 2012, Article ID 845618, pages 1-10.

Huntington's disease (HD) is a neurodegenerative disorder caused by a genetic mutation in the IT15 gene, leading to cognitive dysfunction and abnormal body movements called chorea. HD is characterized by progressive neurodegeneration of the striatum but also involves other regions, primarily the cerebral cortex. Like other neurodegenerative diseases, HD animal models are typically either toxin-induced models or genetic models. Toxin-induced models (e.g., those based on 3-nitropropionic acid and quinolinic acid) are used to study mitochondrial impairment and excitotoxicity-induced cell death, which are both mechanisms of degeneration seen in the HD brain. The discovery of the HD genetic mutation that led to HD in 1993 has led HD animal models that are genetic-based. These models include transgenic and knock-out mice, as well as a model that uses a viral vector to encode the gene mutation in certain areas of the brain. For review, see, e.g., Ramaswamy et al., ILAR J 2007; 48(9):356-373.

A compound may be optionally tested in at least one additional animal model (see, generally, Immunologic Defects in Laboratory Animals, eds. Gershwin et al., Plenum Press, 1981), for example, such as the following: the SWR X NZB (SNF1) mouse model (Uner et al., J. Autoimmune Disease, 1998, 11(3):233-240), the KRN transgenic mouse (K/BxN) model (Ji et al., Immunol. Rev., 1999, 69:139); NZB X NZW (B/W) mice, a model for SLE (Riemekasten et al., Arthritis Rheum., 2001,) 44(10):2435-2445); the NOD mouse model of diabetes (Baxter et al., Autoimmunity, 1991, 9(1):61-67), etc.).

Combination Therapy

The invention further includes treating a subject having a neurodegenerative disease by combination therapy. For example, the method includes treating (e.g., orally administering to) a subject having or at risk of developing a neurodegenerative disease with a compound of formula (I) and one or more other compounds of formula (I) or one or more other therapeutic agents.

In one embodiment, the one or more other therapeutic agents is a disease modifying agent. In one embodiment, the one or more other therapeutic agents alleviate the side effects of the compound of formula (I). For example, if a compound of formula (I) causes side effects such as flushing or GI disturbance (e.g., diarrhea), the one or more other therapeutic agent can be a therapeutic agent that can reduce the flushing (e.g., aspirin) or GI disturbance (e.g., loperamide).

In one embodiment, the combination therapy requires orally administering two compounds wherein at least one of the two compounds is a compound of formula (I). In one embodiment, the subject can be treated with two compounds of formula (I). In one embodiment, the subject can be treated with a compound of formula (I) and DMF, MMF, or a DMF/MMF prodrug

In one embodiment, the first compound and the second compound may be administered concurrently (as separate compositions or together in a single dosage form) or consecutively over overlapping or non-overlapping intervals. In the sequential administration, the first compound and the second compound can be administered in any order. In some embodiments, the length of an overlapping interval is more than 2, 4, 6, 12, 24, 48 weeks or longer.

In one embodiment, the compound of formula (I) and the one or more other therapeutic agents can be used to treat MS. The one or more other therapeutic agents can be, e.g., interferon beta-1a (Avonex®, Rebif®), glatiramer (Copaxone®), modafinil, azathioprine, predisolone, mycophenolate, mofetil, mitoxantrone, natalizumab (Tysabri®), sphinogosie-1 phosphate modulator e.g., fingolimod (Gilenya®), and other drugs useful for MS treatment such as teriflunomide (Aubagio®), piroxicam, and phenidone.

In one embodiment, the compound of formula (I) and the one or more other therapeutic agents can be used to treat ALS. The one or more other therapeutic agents is an agent or agents known or believe to be effective for ALS treatment, e.g., riluzole and dexpramipexole.

In one embodiment, the compound of formula (I) and the one or more other therapeutic agents can be used to treat AD. The one or more other therapeutic agents is an agent or agents known or believe to be effective for AD treatment, e.g., rosiglitazone, roloxifene, vitamin E, donepezil, tacrine, rivastigmine, galantamine, and memantine.

In one embodiment, the compound of formula (I) and the one or more other therapeutic agents can be used to treat PD. The one or more other therapeutic agents is an agent or agents known or believe to be effective for PD treatment include dopamine precursors such levodopa, dopamine agonists such as bromocriptine, pergolide, pramipexole, and ropinirole, MAO-B inhibitors such as selegiline, anticholinergic drugs such as benztropine, trihexyphenidyl, tricyclic antidepressants such as amitriptyline, amoxapine, clomipramine, desipramine, doxepin, imipramine, maprotiline, nortriptyline, protriptyline, amantadine, and trimipramine, some antihistamines such as diphenhydramine; antiviral drugs such as amantadine.

Useful drugs for treating symptoms of Huntington's disease further include selective serotonin reuptake inhibitors (SSRI) such as fluoxetine, paroxetine, sertraline, escitalopram, citalopram, fluvosamine; norepinephrine and serotoiun reuptake inhibitors (NSR1) such as venlafaxine and duloxetine.

Dosages

Pharmaceutical compositions provided by the present invention include compositions wherein the active ingredient is contained in a therapeutically effective amount, i.e., in an amount effective to achieve its intended purpose (reduce or prevent neurodegeneration or neuroinflammation). The actual amount effective for a particular application will depend, inter alia, on the condition being treated.

The dosage and frequency (single or multiple doses) of compound administered can vary depending upon a variety of factors, including route of administration; size, age, sex, health, body weight, body mass index, and diet of the recipient; nature and extent of symptoms of the disease being treated (e.g., the disease responsive to Nrf2 activation); presence of other diseases or other health-related problems; kind of concurrent treatment; and complications from any disease or treatment regimen. Other therapeutic regimens or agents, as mentioned above, can be used in conjunction with the methods and compounds of the invention.

In one embodiment, at least one compound of formula (I) or pharmaceutically acceptable salt thereof is administered in an amount and for a period of time sufficient to reduce or prevent neurodegeneration and neuroinflammation in the subject. In one embodiment, at least one compound is administered in an amount and for a period of time sufficient to reduce astrogliosis, demyelination, axonal loss, and/or neuronal death in the subject. In one embodiment, the at least one compound or pharmaceutically acceptable salt thereof is administered in an amount and for a period of time sufficient to provide neuroprotection (e.g., restoring or increasing myelin content) to the subject.

Methods of the invention may include treating the subject having a neurodegenerative disease with a therapeutically effective amount of at least one compound of formula (I), which can range from about 1 mg/kg to about 50 mg/kg (e.g., from about 2.5 mg/kg to about 20 mg/kg or from about 2.5 mg/kg to about 15 mg/kg). Effective doses will also vary, as recognized by those skilled in the art, dependent on route of administration, excipient usage, and the possibility of co-usage with other therapeutic treatments including use of other therapeutic agents. In one embodiment, an effective dose of a compound of formula (I) to be administered to a subject, for example orally, can be from about 0.1 g to about 1 g per day, for example, from about 200 mg to about 800 mg per day (e.g., from about 240 mg to about 720 mg per day; or from about 480 mg to about 720 mg per day; or about 480 mg per day; or about 720 mg per day). The daily doses may be administered in separate administrations of 2, 3, 4, or 6 equal doses. In one embodiment, the effective daily dose is about 720 mg per day and is administered in 3 equal doses to a subject in need thereof (i.e., three times a day, TID). In one embodiment, the effective daily dose is about 480 mg per day and is administered in 2 equal doses to a subject in need thereof (i.e., two times a day, BID). In one embodiment, the therapeutically effective dose of a compound of formula (I) is administered to a subject in need thereof for a period of time sufficient to reduce neurodegeneration and/or neuroinflammation, e.g., by at least 30%, 50%, 100% or higher over a control over a period of at least 5, 10, 12, 20, 40, 52, 100, or 200 weeks.

In one embodiment, the pharmaceutical composition is administered at least one hour before or after food is consumed by the subject in need thereof. In case the subject experiences side effects (e.g., flushing or GI discomfort), the subject can consume food shortly (e.g., 30 mins to an hour) before administered the pharmaceutical composition.

In one embodiment, the subject administered a compound of formula (I) may take one or more non-steroidal anti-inflammatory drugs (e.g., aspirin) before (for example, 10 minutes to an hour, e.g., 30 minutes before) taking the pharmaceutical composition. In one embodiment, the subject administered the pharmaceutical composition takes the one or more non-steroidal anti-inflammatory drugs (e.g., aspirin) to control side effects (e.g., flushing). In another embodiment, the one or more non-steroidal anti-inflammatory drugs is selected from a group consisting of aspirin, ibuprofen, naproxen, ketoprofen, celecoxib, MK-0524, and combinations thereof. The one or more non-steroidal anti-inflammatory drugs can be administered in an amount of about 50 mg to about 500 mg before taking the dosage form described above. In one embodiment, a patient takes 325 mg aspirin before taking each dosage form described above.

In one embodiment, the pharmaceutical preparation further comprises administering to the patient a first dose of the pharmaceutical preparation for a first dosing period; and administering to the patient a second dose of the pharmaceutical preparation for a second dosing period. one embodiment, the first dose is lower than the second dose (e.g., the first dose is about half of the second dose). In one embodiment, the first dosing period is at least one week (e.g., 1-4 weeks). In one embodiment, the first dose of the pharmaceutical preparation comprises about 120 mg of a compound of formula (I) and the pharmaceutical preparation is administered to the patient BID or TID (e.g., BID) for the first dosing period. In one embodiment, the second dose of the first pharmaceutical preparation comprises about 240 mg of a compound of formula (I) and the first pharmaceutical preparation is administered to the patient BID or TID (e.g., BID) for the second dosing period. In one embodiment, if the subject, after being administered the dose at the second dosing period, experiences more than expected level of side effects (e.g., flushing or a gastrointestinal disturbance), the subject can use a lower dose (e.g., the dose at the first dosing period) for a period (e.g., 1-4 weeks or more) sufficient to allow the side effects to decrease before returning to the dose at the second dosing period.

In order that the invention described herein may be more fully understood, the following examples are set forth. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting this invention in any manner.

EXAMPLES

As depicted in the Examples below, in certain exemplary embodiments, compounds are prepared according to the following general procedures. It will be appreciated that, although the general methods depict the synthesis of certain compounds of formula (I), the following general methods, and other methods known to one of ordinary skill in the art, can be applied to all compounds and subclasses and species of each of these compounds, as described herein.

Example 1 (²H₆)dimethyl fumaric acid ester

To a solution of fumaric acid 1 (1.16 g, 10 mmol) in CD₃OD (1.8 g, 50 mmol, 5.0 eq) was added p-TsOH (0.17 g, 1.0 mmol, 0.1 eq). The reaction mixture was stirred at 80° C. for 6 hours, cooled to room temperature, diluted with EtOAc (50 mL), and washed with saturated NaHCO₃ (20 mL×2) and brine (20 mL). The organic layer was dried over anhydrous Na₂SO₄ and concentrated to give the titled compound, (²H₆)dimethyl fumaric acid ester (0.97 g, yield: 65%) as a white solid. ¹H NMR (DMSO-d₆, 400 MHz) δ ppm: 6.78 (s, 2H); HPLC: 99.46%.

Example 2 (²H₃)methyl fumaric acid ester

To a solution of fumaric acid 1 (1.16 g, 10 mmol) in CD₃OD (1.8 g, 50 mmol, 5.0 eq) was added p-TsOH (0.17 g, 1.0 mmol, 0.1 eq). The reaction mixture was stirred at rt for 48 hours, diluted with H₂O (15 mL) and adjust pH to 10 with 1N aqueous Na₂CO₃. The mixture was extracted with EtOAc (10 mL×3). The aqueous layer was adjusted to pH=1 with 1N HCl and extracted with EtOAc (20 mL×3). The combined organic layers were dried over anhydrous Na₂SO₄ and concentrated to give the crude product, which was recrystallized from THF (5 mL) to give the titled compound, (²H₃)methyl fumaric acid ester (0.73 g, yield: 55%) as a white solid. ¹H NMR (CDCl₃, 400 MHz) 5 ppm: 13.27 (br, 1H), 6.70 (s, 2H); ESI-MS (M+H)⁺: 134.1; HPLC: 100.00%.

Example 3 (²H₃)dimethyl fumaric acid ester

To a solution of (²H₃)methyl fumaric acid ester Ex.2, available from Example 2 (1 equiv.) in dichloromethane is added EDCI (1.5 equiv.), HOBt (1.5 equiv.), and DIPEA (2.0 equiv.). Methanol (1.2 equiv.) is added. The mixture is to be stirred overnight at room temperature, and then diluted with dichloromethane, to be washed with H₂O and brine. The organic layer should be dried over Na₂SO₄. Removal of solvent should afford the titled compound, which can be purified by recrystallization to give the pure product of (²H₃)dimethyl fumaric acid ester.

Example 4 dimethyl fumaric(2,3-²H₂) acid ester

To a solution of fumaric(2,3-²H₂) acid 3 (0.2 g, 1.7 mmol) in methanol/diethyl ether (20/10 mL) was added (trimethylsilyl)diazomethane (3.2 mL, 6.4 mmol) dropwise. The mixture was stirred at room temperature overnight. Solvents were removed in vacuo, the residue was purified by column chromatography (PE/EA=80:1) to give the titled compound as a white solid (0.1 g, yield: 40%) ¹H NMR (300 MHz, CDCl₃) δ 3.81 (s, 6H). LC-MS: m/z=147.1 [M+H]⁺. HPLC: 99.8% (214 nm); 100% (254 nm).

Example 5 Evaluation of the Pharmacokinetic Properties of the Compound of Example 1 with DMF

General procedure: Compounds were dosed in 0.5% HPMC suspension at 100 mg/Kg or a specific dose equivalent to male SD rats via oral gavage. Plasma samples were collected at 8 time points, 5 min, 15 min, 30 min, 1 h, 2 h, 4 h, 6 h and 12 h. Brain and CSF samples were collected at 30 min, 2 h, 4 h, and 6 h. The samples were preserved by adding 2 mM PMSF and 1% acetic acid (final concentrations) during blood and CSF sample collection, and brain tissue homegenization. The concentration of the compounds was determined by LC/MS/MS.

Example 1 was dosed in 0.5% HPMC suspension @ 104 mg/kg (90 mg/kg MMF-eq) to male SD rats via oral gavage. Plasma samples were collected at 5 minutes, 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 6 hours and 12 hours and processed according to the above procedure. The concentration of D-MMF was determined by LC/MS/MS. Brain and CSF samples were collected at 30 min, 2 hr, 4 hr and 6 hr. The concentration of D-MMF was determined by LC/MS/MS.

Example 6 Evaluation of Nrf2 Activation Effects: Cell-Based Assay

Human cancer cell line DLD-1 and breast cancer cell line MCF7 reporter stable cell lines were generated by transfection with a firefly luciferase reporter construct harboring the luciferase cDNA cloned downstream of eight catenated copies of the antioxidant response element (ARE) (GACAAAGCACCCGT; SEQ ID NO.:1). See Wang et al. Cancer Res. 2006; 66:10983-94.

To measure Nrf2 activation in the ARE-luciferase reporter cell lines, the cells were plated in 96-well plates at 20-50 k cells/well 24 hours prior to stimulation with the test compounds. The test compounds were prepared in dimethylsulfoxide (DMSO) and diluted with culture media to required concentrations (final DMSO concentrations <0.3%). The reporter cells were harvested 24 hours-48 hours after addition of the compounds and lysed for detection of luciferase activity. Luciferase activity in the lysates was monitored using the Bright-Glo Luciferase Assay System of Promega and Tecan Genios Pro plate reader.

Luciferase induction in the compound-treated cells was calculated as fold change over the baseline activity detected in control cultures treated with DMSO-containing media.

Nrf2 Activation in DLD-1 and MCF-7 ARE-Luc Reporter Cell Line

EC50 [uM] at 48 hr Stimulation (D-DMF: Example 1; D-MMF: Example 2) Maximum Nrf2 Activation Fold Change upon Compound Stimulation:

24 hr Stimulation 48 hr Stimulation MCF- MCF- DLD-1/ARE-E2 7/ARE-D3 DLD-1/ARE-E2 7/ARE-D3 Fold Fold Fold Fold Change @ [uM] Change @ [uM] Change @ [uM] Change @ [uM] DMF 3 31 25 63 9 31 68 94 MMF 5 1000 75 1000 12 1000 94 750 Compound 2 31 29 63 8 31 65 94 from Ex. 1 Compound 6 1000 55 1000 14 1000 81 1000 from Ex. 2

The data above indicates that compounds of Examples 1 and 2 are able to activate ARE-dependent signaling of the luciferase reporter construct. This suggests the compounds are able to activate the Nrf2 signaling cascade and induce expression of genes downstream of the ARE.

Example 7 In Vivo Evaluation of Nrf2 Activation

Test compounds were dosed either in suspension of 0.8% HPMC or corn oil via oral gavage to male SD rats (average weight of 250 mg, 6 animals per group, two groups), at a dose of 100 mg/kg equivalent of DMF (dosing volume: 5 ml/kg). After 30 minutes, the first group of animals was sacrificed via CO2 asphyxiation. 1.0 mL blood sample via cardiac bleed pipetted into chilled lithium heparin tubes with 10 mg sodium fluoride. Samples were centrifuged within 30 minutes at 4° C. for 15 minutes at 1500 G and plasma was transferred to chilled tubes and immediately frozen on dry ice, further kept at −70° C. until shipment for analysis. Brain was removed; sections were weighed and frozen until analysis. Brain and plasma samples were analyzed for (²H₃)methylfumaric acid ester (MMF) exposure. After 6 hours, the second group of animals was sacrificed via CO2 asphyxiation. Brain, spleen, liver and jejunum were removed, flash frozen and placed on dry ice and maintained frozen until analysis. Sections of brain, spleen, liver, and jejunum were submitted for qPCR analysis of relative expression increase of Nrf2 responsive enzymes such as NQO-1, Akr1b8, and Sulfiredoxin-1. See results in FIGS. 1( a)-(c).

Having now fully described this invention, it will be understood by those of ordinary skill in the art that the same can be performed within a wide and equivalent range of conditions, formulation and other parameters without affecting the scope of the invention or any embodiment thereof. All patents, patent applications and publications cited herein are fully incorporated by reference herein in their entirety.

All publications and patent documents cited herein are incorporated by reference in their entirety. To the extent the material incorporated by reference contradicts or is inconsistent with the present specification, the present specification will supersede any such material. 

1. A compound of formula (I)

or a pharmaceutically acceptable salt thereof, wherein each of R¹ and R², independently, is hydrogen, deuterium, deuterated methyl, deuterated ethyl, C₁₋₆ aliphatic, phenyl, 3-7 membered saturated or partially unsaturated monocyclic carbocyclic ring, 3-7 membered saturated or partially unsaturated monocyclic heterocyclic ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, or a 5-6 membered heteroaryl ring having 1-3 heteroatoms independently selected from nitrogen, oxygen, and sulfur, and each of R³ and R⁴, independently, is hydrogen or deuterium, provided that the compound of formula (I) contains at least one deuterium atom and that R¹ and R² are not hydrogen at the same time.
 2. The compound of claim 1, wherein R¹ is hydrogen or —CH₃.
 3. The compound of claim 2, wherein R² is —CH₂D, —CHD₂, or —CD₃.
 4. The compound of claim 1, wherein R¹ is —CD₃.
 5. The compound of claim 4, wherein R² is —CH₂D, —CHD₂, or —CD₃.
 6. The compound of claim 1, wherein at least one of R³ and R⁴ is deuterium.
 7. The compound of claim 6, wherein both of R³ and R⁴ are deuterium.
 8. The compound of claim 6, wherein R² is hydrogen, —CH₃, —CH₂D, —CHD₂, or —CD₃.
 9. The compound of claim 1, wherein R¹ is —CD₂CD₃.
 10. The compound of claim 9, wherein R² is H, —CH₃, —CH₂D, —CHD₂, or —CD₃.
 11. A compound of formula (I) wherein the compound is (²H₆)dimethyl fumaric acid ester, (²H₃)methyl fumaric acid ester, (²H₃)dimethyl fumaric acid ester, or dimethyl fumaric(2,3-²H₂) acid ester.
 12. A method of activating the Nrf2 pathway, comprising contacting cells with a sufficient amount of a compound of claim
 1. 13. A method of treating a neurodegenerative disease, comprising administering to a subject in need of treatment for the neurodegenerative disease an effective amount of a compound of claim
 1. 14. The method of claim 13, wherein the neurodegenerative disease is MS, ALS, Parkinson's disease, Huntington's disease, or Alzheimer's disease. 